Generisanje superkontinuuma i primena u optičkim telekomunikacijama

Supercontinuum generation is a phenomenon ofsignal spectrum broadening, due to the interplay between nonlinear and dispersive effects of the nonlinear medium. This phenomenon has been the subject of numerous studies in different mediums, due to its wide range of applications in a number of fields, such as tomography, metrology, spectroscopy, biomedical optics and in the field of optical telecommunications. For the analysis and modeling of the supercontinuum characteristics, it is crucial to select a medium in which signal propagation and supercontinuum generation are performed. For the application of supercontinuum in the field of optical telecommunications, optical fibers of the specific microstructure, i.e.PCF (Photonic Crystal Fiber) fibers are used, due to the high nonlinearity and the ability to model its dispersion profile, by modeling the structure of the fiber itself. In addition to the dispersive and nonlinear characteristics of the fiber, characteristics of the supercontinuum spectrum depend on a number of input signal parameters, such as wavelength, power, shape and duration of the input pulse. These parameters significantly influence the dynamics of the supercontinuum, in terms of the formation of processes responsible for the generation of supercontinuum, such as soliton fission, dispersive waves generation, self-phase modulation, etc. On the other hand, they also affect the width of the supercontinuum output spectrum and its coherence, which is crucial for supercontinuum applications in different fields. This doctoral thesis presents the investigation of supercontinuum characteristics in PCF fibers of different dispersion profiles, for different input signal parameters. Supercontinuum generation is performed at wavelengths corresponding to the first, second and third optical windows. The processes responsible for spectrum spread in different optical windows and dispersion regimes, for different values of the input parameters, are analyzed. Supercontinuum generation in PCF fibers is numerically investigated and the process itself was modeled by the nonlinear Schrödinger equation. Also, the thesis gives an overview of the probability of distribution of extreme events, RW (Rogue Wave) waves, in supercontinuum generated in the anomalous dispersion regime. Furthermore, study was focused on determining the characteristics of the supercontinuumspectrum and its coherence in the anomalous and normal dispersive regime, in order to define the optimaldispersion regime, the type of PCF fiber and the input parameters of the signal, to obtain supercontinuum spectrum, suitable for use as a multi-wavelength optical source in WDM (Wavelength Division Multiplexing) systems

Strong coupling regime of semiconductor quantum dot embedded in the nano-cavity

Photonic lattices represent suitable systems for investigation of wave propagation in periodic structures [1]. However, different unavoidable defects may arise either during their process of fabrication or as result of misusage, accidental damage, etc. Although undesirable in the first place, these imperfections enable the existence of different types of stable, localized defect modes [2]. In this paper, we investigate light propagation through composite photonic lattice composed of two identical linear and lossless lattices. The interface between them represents a geometric defect, while each lattice contains a single nonlinear defect that is placed symmetrically with respect to the interface. Depending on the input light beam parameters (its position, width and transverse tilt), the width of geometric defect, strength and position of the nonlinear defects, different dynamical regimes have been identified. These dynamical regimes are caused by the balance of photonic lattice potentials’ contributions originating from the presence of the geometric and two nonlinear defects. We have found numerically conditions under which dynamically stable bounded modes can exist in the area between nonlinear defects or between a nonlinear and a geometric defect. Various types of localized modes such as: two-hump, multi-hump, one- and multicomponent moving breathers localized at a certain area among defects have been observed. The parameters can be adjusted to capture light and to prevent light launched inside the area among defects to leave it, i.e. this corresponds to the appearance of the modes trapped inside this area. Since the configuration of the lattice prevents transmission of the light through the area confined by defects, these modes can formally be related to Fano resonances and Fano- blockade [3, 4]. When light is launched outside the area among defects, different dynamical regimes have been distinguished: total reflection, single and double partial reflection and full transmission through the area among defects. These numerical findings may lead to interesting applications such as blocking, filtering and transporting light beams through the optical medium. Photonic devices based on resonant tunneling such as waveguides interacting through the area between defects, may be applied as add-drop filters.V International School and Conference on Photonics and COST actions: MP1204, BM1205 and MP1205 and the Second international workshop "Control of light and matter waves propagation and localization in photonic lattices" : PHOTONICA2015 : book of abstracts; August 24-28, 2015; Belgrad

Carbon dioxide activation of the plane tree seeds derived bio-char: Kinetic properties and application

Goal of this work is to establish technical feasibility and fundamentals of producing activated carbon from plane tree seeds biomass for porous materials derivation. Bio-chars produced via carbonization from plane tree seeds precursor were activated in CO2 at 750 and 850?C, during various residence times. Their surface area and porosity were characterized by N2 adsorption at 77 K. Surface areas of activated carbons can be correlated with kinetics mechanism and activation energy magnitudes of oxidation reaction by CO2, which are closely related to applied activation temperature. Result showed that high temperature activated carbon had higher gas adsorption as compared to activated carbon obtained from lower temperature during two-hour residence time. Breakthrough behavior was detected at 850?C where surface reactions dominate, and it is characterized by autocatalytic kinetic model under designed conditions. Both, temperature and CO2 concentration in vicinity of solid surface effect on breakthrough time of adsorbent. Derived bio-chars are converted into high quality activated carbons, with surface area of 776.55 m2/g, where micro-pores with pore diameters less than 2 nm prevail. Produced activated carbons have properties comparable with commercially available activated carbons, which can be successfully used for removal of harmful gaseous pollutants toward air purification

Preparation of Active Carbon Material By Activation With Various Hydroxide And Characterization Of Their Properties

The aim of this research is to obtain active carbon material from the plane tree fruit. The precursor was first treated with hydrothermal synthesis and then mechanochemically activated with various hydroxides and finally carbonization was done to promote activation.It can be concluded that by acting of different hydroxides (NaOH, BaOH, LiOH, KOH) in the same mass ratio and using the same precursor and the same process, totally different materials with different structure and morphology are obtained.The initial composition of the precursor as well as the final product (active carbon materials) were analyzed using a proximative and ultimate method. The active area surface, volume and pore size was determined using the BET method. Verification of surface-active reaction groups in the identified structures was carried out through Fourier-transform infrared (FTIR) spectroscopy. Morphology of resulting activated carbon materials has been investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The application of the obtained materials is reflected in the fact that we removed the waste, we prevented the pollution of nature, and on the other hand we have obtained material that can be used for various purposes, for example, air and water filters, heating briquettes, fertilizer for plants, superconductors, etc.IX Serbian Ceramic Society Conference - Advanced Ceramics and Application : new frontiers in multifunctional material science and processing : program and the book of abstracts; September 20-21, 2021; Belgrad

Generisanje superkontinuuma i primena u optičkim telekomunikacijama

Supercontinuum generation is a phenomenon ofsignal spectrum broadening, due to the interplay between nonlinear and dispersive effects of the nonlinear medium. This phenomenon has been the subject of numerous studies in different mediums, due to its wide range of applications in a number of fields, such as tomography, metrology, spectroscopy, biomedical optics and in the field of optical telecommunications. For the analysis and modeling of the supercontinuum characteristics, it is crucial to select a medium in which signal propagation and supercontinuum generation are performed. For the application of supercontinuum in the field of optical telecommunications, optical fibers of the specific microstructure, i.e.PCF (Photonic Crystal Fiber) fibers are used, due to the high nonlinearity and the ability to model its dispersion profile, by modeling the structure of the fiber itself. In addition to the dispersive and nonlinear characteristics of the fiber, characteristics of the supercontinuum spectrum depend on a number of input signal parameters, such as wavelength, power, shape and duration of the input pulse. These parameters significantly influence the dynamics of the supercontinuum, in terms of the formation of processes responsible for the generation of supercontinuum, such as soliton fission, dispersive waves generation, self-phase modulation, etc. On the other hand, they also affect the width of the supercontinuum output spectrum and its coherence, which is crucial for supercontinuum applications in different fields. This doctoral thesis presents the investigation of supercontinuum characteristics in PCF fibers of different dispersion profiles, for different input signal parameters. Supercontinuum generation is performed at wavelengths corresponding to the first, second and third optical windows. The processes responsible for spectrum spread in different optical windows and dispersion regimes, for different values of the input parameters, are analyzed. Supercontinuum generation in PCF fibers is numerically investigated and the process itself was modeled by the nonlinear Schrödinger equation. Also, the thesis gives an overview of the probability of distribution of extreme events, RW (Rogue Wave) waves, in supercontinuum generated in the anomalous dispersion regime. Furthermore, study was focused on determining the characteristics of the supercontinuumspectrum and its coherence in the anomalous and normal dispersive regime, in order to define the optimaldispersion regime, the type of PCF fiber and the input parameters of the signal, to obtain supercontinuum spectrum, suitable for use as a multi-wavelength optical source in WDM (Wavelength Division Multiplexing) systems

Numerical study of high intensity events in the supercontinuum generation in the presence of input chirp

We examine the supercontinuum (SC) dependence on the chirp of the input laser beam and effects of input pulse noise. Simultaneously, we investigate the relation between the SC generation and creation of localized high intensity events. We show that despite their low probability, these events inevitably appear in the SC in our setup. Their devastating role in the information transfer stimulates the research aiming for a deeper understanding of these phenomena which is of high importance in different fields of science, ranging from material science to telecommunications. This study can be considered as a step forward in tracing a route for controlling high intensity events. © 2019 Elsevier Gmb

Application of Model-Free and Model-Based Kinetic Methods in Evaluation of Reactions Complexity during Thermo-Oxidative Degradation Process: Case Study of [4-(Hydroxymethyl)phenoxymethyl] Polystyrene Resin

This work examined the possibilities and limitations of model-free and model-based methods related to decrypting the kinetic complexity of multi-step thermo-oxidative degradation processes (as a testing system, a [4-(hydroxymethyl)phenoxymethyl] polystyrene resin was used), monitored by thermal analysis (TGA-DTG-DTA) techniques. It was found that isoconversional methods could successfully determine the correct number of process stages and presence of multiple reactions based on derived Ea(α) profiles and identify the negative dependence of the rate constant on the temperature. These methods could not overcome the problem that arose due to mass transfer limitations. The model-based method overcame more successfully the problem associated with mass transfer because its calculation machinery had capabilities for the correct solution of the total mass balance equation. However, a perfect fit with the experimental data was not achieved due to the dependence on the thermal history of the contribution (ctb.) of a given reaction step inside a fitting procedure cycle. On the other hand, through this approach, it was possible to estimate the rate-controlling steps of the process regarding the influence of the heating rate. It was found that for consecutive reaction mechanisms, the production of benzaldehyde and gases in high yields was controlled by the heating rate, where low heating rates were strongly recommended (≤10 K/min). Also, it was shown that the transport phenomenon may be also the rate-determining step (within the set of “intrinsic” kinetic parameters). It was also established that external heat transfer controls the overall rate, where the “pure” kinetic control regime had not been reached but was approached when lowering the temperature and size of the resin particles

Chaotic dynamics and supercontinuum generation with cosh-Gaussian pulses in photonic-crystal fibers

In this paper, we investigate broadband supercontinuum generation in photonic crystal fibers using cosh-Gaussian optical pulses, which provide flatter spectrum than standard Gaussian pulses. This fact can be crucial for telecommunication systems applications. The intensive numerical study of three main telecommunication windows pointed out the most prominent window for spectral broadening. This finding offers the possibility of improving the characteristics of multi-wavelength sources and to enable wavelength density multiplexing systems

Gold chloride cluster ions generated by vacuum laser ablation

In this work we have studied the vapor species which are generated by pulsed Nd:YAG laser ablation of chloroauric acid (HAuCl4) in the absence of a buffer or reactive atmosphere and without postablation supersonic expansion. The laser ablation of HAuCl4 into vacuum generates significant yields of gold chloride cluster ions, the compositions of which were analyzed by time-of-flight mass spectrometry with a commercial matrix assisted laser desorption/ionization (MALDI) instrument. Pulsed laser ablation and vaporization of solids have found wide application in the deposition of thin films of a wide variety of materials for various purposes such as producing a high-quality semiconductor films for electronic and optoelectronic devices [1]. For this reason many laser ablation studies have been focused on the properties and performance of such deposited materials. Also, a large efforts have aimed at characterizing laser-solid interactions and ablation vapor plume [2]. On the other side, the laser ablation it has been successfully applied for generating novel and large vapor cluster species such as homogenous and heterogeneous metal clusters [3]. Earlier results have shown that the ablation of laser–gold nanofilm (Au NF) under irradiation with a nanosecond pulsed laser probably follows a photothermal evaporation mechanism, in which absorption of laser energy by the Au NF leads to formation of Au-nanoparticles via spinodal dewetting, followed by surface melting, and eventually a decrease in size or splitting, due to evaporation from surface atoms or the entire particle. The formation of Au cluster ions during the evaporation of Au NFs is accompanied by electron ejection [4]. Gold halide clusters have significant applications in catalysis, optics, medicaments, and environmental sciences. This work shows the possible formation of gold chloride cluster ions by the laser ablation. A small volume (0.5 μl) of HAuCl4 solution was applied onto the stainless-steel sample plate and left to dry at room temperature. Different concentration of HAuCl4 solution were analyzed, such as: 2,5 g Au/dm3 (initial solution), 0,25 g Au/dm3, and 0,025 g Au/dm3. The laser intensity was varied between 4000-5000 a.u. and the average of 1800 laser shots were taken for each spectrum. Preliminary results shows the formation of negative gold chloride cluster ions, such as: AuCl(HCl)(H2O), AuCl2, AuCl2(HCl)2H2O, AuCl2(HCl)2(H2O)3, AuCl2(HCl)2(H2O)4, AuCl2(HCl)3(H2O)3, Au2Cl(HCl)3H2O, Au2Cl(HCl)3(H2O)3, AuCl2(HCl)3(H2O)4, Au2Cl(HCl)5H2O, AuCl3(HCl)2(H2O)5, Au2Cl(HCl)6H2O, AuCl4(HCl)4, Au2Cl(HCl)5(H2O)2, Au2Cl2(HCl)6(H2O)5. Concerning different concentrations, the spectra have shown that the intensities of these complex composition clusters, [AuxCly(HCl)m(H2O)n], formed from the HAuCl4 increase with decreasing the concentration of HAuCl4 solution.VI International School and Conference on Photonics and COST actions: MP1406 and MP1402 : PHOTONICA2017 : August 23 - September 1, 2017; Belgrade

Modeling and optimization of sunflower oil methanolysis over quicklime bits in a packed bed tubular reactor using the response surface methodology

The effect of the residence time (i.e. liquid flow rate through the reactor), methanol-to-oil molar ratio and reaction temperature on the fatty acid methyl esters (FAMEs) content at the output of a continuous packed bed tubular reactor was modeled by the response surface methodology (RSM) combined with the 3(3) full factorial design (FFD) with replication or the Box-Behnken design (BBD) with five center points. The methanolysis of sunflower oil was carried out at the residence time of 1.0, 1.5 and 2.0 h, the methanol-to-oil molar ratios of 6:1, 12:1 and 18:1 and the reaction temperature of 40, 50 and 60 degrees C under the atmospheric pressure. Based on the used experimental designs, the model equations containing only linear and two-factor interaction terms were developed for predicting the FAME content, which were validated through the use of the unseen data. Applying the analysis of variance (ANOVA), all three factors were shown to have a significant influence on the FAME content. Acceptable statistical predictability and accuracy resulted from both designs since the values of the coefficient of determination were close to unity while the values of the mean relative percentage deviation were relatively low ( LT +/- 10%). In addition, both designs predicted the maximum FAME content of above 99%, which agreed closely with the actual FAME content (98.8%). The same optimal reaction temperature (60 degrees C) and residence time (2.0 h) were determined by both designs while the BBD model suggested a slightly lower methanol-to oil molar ratio (12.2:1) than the 3(3) FFD model (12.8:1). Since the BBD realization involved three times smaller number of experimental runs, thus requiring lower costs, less labor and shorter time than the 33 FFD, it could be recommended for the optimization of biodiesel production processes